Commonly-owned U.S. Pat. No. 5,660,802 to Archer, et al., the contents of which are incorporated herein in their entirety by this reference, discloses multiple embodiments of water purification equipment. Included as parts of the equipment are housings, or vessels, having both fluid inlets and outlets. Pressurized fluid (water) flows through an inlet into a body housing, typically, a purification unit, with at least some of the fluid contacting material within the purification unit for treatment.
As noted in the Archer patent:                The water inlet and water outlet are incorporated into a body to which is connected a cover that houses the purification unit. This cover is removable for replacement of the purification unit . . .See Archer, col. 2, 11. 17–20. In at least some embodiments of the vessels disclosed in the Archer patent, the cover “is typically threaded and . . . includes several ridges that provide gripping surfaces that ease [its] attachment . . . to the body.” See id., col. 3, 11. 63–65 (numeral omitted).        
U.S. Pat. No. 5,993,753 to Davidson discusses a two-chambered chemical feeder assembly having an inlet, an outlet, and a housing. Included as part of the housing is a cap having                an outer annular shoulder, a threaded outer cover and an open, flanged, internally threaded tube in the center of the cap. The outer cover threadedly engages the internally threaded tube, thereby compressing an o-ring effecting a fluid-tight seal between the outer cover and the cap.See Davidson, col. 3, 11. 46–51 (numerals omitted).        
U.S. Pat. No. 4,617,117 to Messinger, et al. details another assembly for pressurized fluids incorporating an inlet, an outlet, and a housing. According to the Messinger patent, the assembly includes “a cover removably attached to the housing in a manner that allows jacking of the cover into and away from sealing engagement with the housing.” See Messinger, Abstract, 11. 2–4. A central boss extends outwardly from the cover and has an external cylindrical wall functioning as a bearing surface. The assembly additionally includes a jack ring whose center embraces the external wall of the boss. As noted in the Messinger patent:                when [a] top cover is threaded onto the housing, it engages the removable cover both at its central position adjacent the central aperture of the ring, in the region of the boss on the removable cover, and also at the external periphery thereof, at the ledge of the top cover bearing against [a] flange [of the removable cover]. The jack ring thus carries the removable cover into tight sealing engagement with the housing, closing off the fluid chamber when it has been fully threaded onto the housing.See id., col. 5, 11. 36–45.        